(a) Technical Field
The present invention discloses a functionalized aromatic organosulfur trans polybutadiene comprising aromatic organosulfur compound chemically bound to the polymeric chain. In particular, high 1,4-trans polybutadiene is prepared in the presence of a particular catalyst, and an aromatic organosulfur compound is directly bound to the polybutadiene. A high 1,4-trans polybutadiene comprises the aromatic organosulfur compound bound to the end of the polymeric chain. The organosulfur molecule existing in molecule chain decreases ultra high polymer region and narrows molecular weight distribution, while remarkably improving processability and physical properties. This results in uniform crosslinking density, thus improving processability, elasticity and mechanical properties if it is used in preparing a rubber composition. Further, it inhibits gelation by preventing oxidation-reduction reaction that may be caused by metals such as cobalt.
(b) Background Art
The technology for preparing 1,4-trans polybutadiene by using butadiene as a monomer has long been known (Rubber Plast. Age, 1963, 44, 42), where butadiene is polymerized into 1,4-trans polybutadiene in the presence of Ziegler-Natta catalyst comprising vanadium compound and alkyl aluminum. This catalyst provides trans-polybutadiene having a relatively high melting point (Tm) of 70-130° C., and the polybutadiene needs to go through with an aging process at high temperature before being mixed with other rubbers or fillers. Beside the vanadium catalyst, other catalysts have also been reported for the manufacture of 1,4-trans polybutadiene.
Japanese patent application No. 67187, which was filed in 1967, discloses a process of preparing polybutadiene with the trans content of 75-80% in the presence of a combined catalyst comprising a cobalt compound, organoaluminum and phenol.
U.S. Pat. No. 5,089,574 discloses a process of preparing 1,4-trans-polybutadiene by the 1,3-butadiene polymerization in the presence of a catalyst comprising cobalt carboxylate, alkylphenol, organoaluminum and CS2. In particular, molecular weight was controlled by using CS2 in this catalyst system. U.S. Pat. No. 5,448,002 discloses a process of preparing 1,4-trans-polybutadiene by the 1,3-butadiene polymerization in the presence of a catalyst comprising cobalt carboxylate, alkylphenol, dialkylsulfoxide and organoaluminum. In particular, molecular weight was controlled by using dialkylsulfoxide in this catalyst system.
U.S. Pat. Nos. 6,310,152 and 6,617,406 disclose a process of preparing 1,4-trans-polybutadiene by the 1,3-butadiene polymerization by using a mixture of cobalt carboxylate, para-alkylphenol or para-alkylphenol and ortho-alkylphenol in combination with organoaluminum as a catalyst. U.S. Pat. No. 5,834,573 discloses a process of preparing 1,4-trans-polybutadiene by the 1,3-butadiene polymerization by using cobalt (oxidation state: +3) acetylacetonate, alkylphenol and organoaluminum as catalysts.
U.S. Pat. Nos. 5,025,059 and 6,608,154 disclose the trans-polybutadiene polymerization by using barium thymolate/trialkylaluminum/alkyl lithium.
The application of 1,4-trans polybutadiene to tire manufacture was disclosed in U.S. Pat. Nos. 5,025,059 (1991), 5,626,697 (1997), 5,753,761 (1998), 6,581,659 and 6,765,063.
The conventional trans polybutadiene has the following drawbacks: (a) relatively high gel content and molecular weight; (b) requirement of pre-heating polymer to a temperature above a melting point by using an oven, etc.; and (c) poor compatibility with other rubbers.